diff --git a/lib/AST/CommentLexer.cpp b/lib/AST/CommentLexer.cpp
index fde2c40..31a09f7 100644
--- a/lib/AST/CommentLexer.cpp
+++ b/lib/AST/CommentLexer.cpp
@@ -226,6 +226,11 @@
   return skipWhitespace(BufferPtr, BufferEnd) == BufferEnd;
 }
 
+bool isCommandNameStartCharacter(char C) {
+  return (C >= 'a' && C <= 'z') ||
+         (C >= 'A' && C <= 'Z');
+}
+
 bool isCommandNameCharacter(char C) {
   return (C >= 'a' && C <= 'z') ||
          (C >= 'A' && C <= 'Z') ||
@@ -340,7 +345,7 @@
         }
 
         // Don't make zero-length commands.
-        if (!isCommandNameCharacter(*TokenPtr)) {
+        if (!isCommandNameStartCharacter(*TokenPtr)) {
           formTextToken(T, TokenPtr);
           return;
         }